In the existing Long Term Evolution (LTE) standard of the 3rd Generation Partnership Project (3GPP), a DL (Downlink) transmission technology is based on Orthogonal Frequency Division Multiplexing (OFDM) while a UL transmission technology is based on Single-Carrier Frequency Division Multiple Access (SC-FDMA). The LTE system uses two types of frame structure, i.e., frame structure type 1 adopting Frequency-Division Duplex (FDD) and frame structure type 2 adopting Time Division Duplex (TDD). Frame structure type 2 includes seven kinds of different frame structure configurations. The proportion of DL sub-frames in each kind of frame structure configuration is fixed, ranging from 40% to 90%. As shown in FIG. 1, sub-frames identified with “D” are DL sub-frames, sub-frames identified with “U” are UL sub-frames and sub-frames identified with “slashes” are special Sub-frames.
The DL data sub-frames Physical Downlink Shared Channel (PDSCH) are used for transmitting DL data, and Acknowledgement (ACK)/Negative Acknowledgement (NACK) information corresponding to the PDSCH is fed back with Physical Uplink Control Channel (PUCCH) of UL control sub-frames. Downlink Control Information (DCI) corresponding to the DL data is borne by a CCE (Control Channel Element) aggregation on a Physical Downlink Control Channel (PDCCH). Existing mapping method of ACK/NACK corresponding to the PDSCH include an implicit mapping method and an explicit mapping method. Where, the implicit mapping method includes:
First, positions of Physical Uplink Control Channel (PUCCH) sub-frames for feeding back the ACK/NACK information are determined according to positions of PDSCH sub-frames. Then, specific resources positions of the ACK/NACK information which is fed back in the corresponding PUCCH sub-frames are determined according to a position of the first CCE in the CCE aggregation of the DCI information bearing the DL data. The above implicit mapping method directly indicates the resource positions of the ACK/NACK without extra information. Thus, overheads are saved and resources utilization rate is enhanced.
In order to further meet the requirement of enhancing data speed, a conception of Carrier Aggregation (CA) is introduced into version 10 (Rel-10) of the LTE. Multiple continuous or discontinuous bandwidth carriers are aggregated into system bandwidth up to 100 Mhz. Specifically, in the LTE Rel-10 system, the UE may be configured with multiple Component Carriers (CC)s. An evolved Node B (eNB) notifies the UE of a number of a Primary CC (PCC) and numbers of aggregated Secondary CCs (SCC)s through high-level signaling. At the same time, along with the development of actual network deployment and system operations, in the future evolution of the Time Division (TD)-LTE system, the problem that different CCs adopts different sub-frame configurations becomes an important problem needing to be taken into account in the evolution of the TD-LTE system.
When the multiple CCs configured for the UE are in different frequency bands, and the frame structure configuration of at least one CC is different from the frame structure of other CCs, how to design a timing relationship between PDSCH of a DL data sub-frame and UL control information, and more specifically how to design the timing relationship between the PDSCH and the ACK/NACK information becomes a key issue to be solved when the carrier aggregation technologies of different bands adopt different frame structure configurations.
At present, on the basis of rational technical analysis, there are mainly two potential technical routes.
The first method for feeding back the ACK/NACK is on an assumption that all UEs supporting a carrier aggregation technology of different bands and characteristics of different frame structure configurations include at least two Power Amplifiers (PA)s and Radio frequency (RF) circuits. When all CCs of the UE are in two different bands and the frame structure configurations in any different band are the same, while the frame structure in different bands is different, the eNB designates a CC for feeding back ACK/NACK information for each UE in each band through the high-level signaling. Each band continues to use an existing timing relationship between the PDSCH and UL ACK/NACK in its band according to its different frame structure configurations. As shown in FIG. 2, the problem of the first method lies in that the costs of the Rel-11 terminals are greatly enhanced, and the realization and markets of the Rel-11 products are restricted. Meanwhile, how to support the power control of cell edge users with limited power and UL ACK/NACK is also a problem to be solved by the first method.
As for the problems of the first method, the second method merely sending the UL ACK/NACK information on a single PCC to ensure that even low-end users with only one PA in the Rel-11 system still can benefit from the carrier aggregation technology of different bands with different frame structure configurations, and continue to use the existing power control mechanism of the UL ACK/NACK information.
In the second method, the typical method is designing a new timing relationship between the PDSCH and UL ACK/NACK. However, a scheduler needs to use a new scheduling policy for allocating and scheduling resources, i.e., the method needs to change the existing scheduler algorithms.
The second method further includes an improved method: The UE determines positions of public UL sub-frames according to the frame structure configurations of configured CCs, searches for and determines a unique and backward compatible frame structure configuration according to the positions of the public UL sub-frames, and at last, maps the specific timing relationship between the PDSCH and UL ACK/NACK out one by one on the PCC configured by the UE according to the determined backward compatible frame structure configuration. The UE uses the above method for effectively supporting the carrier aggregation of Bands of different frame structure configurations and implementing coexistence and performance optimization of different communication systems without limiting the number of amplifiers of the UE. As shown in FIG. 3, when the UE configures two different CCs on two different frequency bands, one of the CC is the PCC adopting frame structure configuration 1, and the other is SCC adopting frame structure configuration 2. The UE decides to feed back the ACK/NACK information corresponding to the PDSCH on the PCC and SCCs adopting the timing relationship between the PDSCH and ACK/NACK defined by frame structure configuration 2 according to the above method.
For the convenience of description, UL sub-frames in any wireless frame are divided into two categories according to whether the ACK/NACK information of Rel-11 is borne. One of the categories specifically indicates UL sub-frames for transmitting the ACK/NACK information of different frame structure configurations on different CCs, and this category is called type I UL sub-frames, and the other UL sub-frames are called type II UL sub-frames. Here, Rel-11 ACK/NACK specifically indicates the ACK/NACK information generated when different CCs adopt different frame structure configurations. More specifically, as shown in FIG. 3, when the cell adopts frame structure 1 on the PCC while adopts frame structure 2 on the SCC, sub-frame 2 and sub-frame 7 in any wireless frame are type I UL data sub-frames, while both sub-frame 3 and sub-frame 8 are type II UL data sub-frames.
As for the wireless frame including the type I and type II UL data sub-frames, the ACK/NACK loads of the type I UL data sub-frames are different from those of the type II UL data sub-frames, resulting in that the UL overheads of the two kinds of UL data sub-frames are different. In the type II UL data sub-frames, since the ACK/NACK causes a relatively light load, thus much more resources are used for transmitting the UL data. That is to say, compared with the type I UL sub-frames, the PUSCH of the type II UL sub-frames occupies much more resources. As shown in FIG. 4, the loads of the ACK/NACK of sub-frames 7 and sub-frame 8 are different, resulting in that the UL overheads of two continuous sub-frames are different. Specifically, in sub-frame 8, the ACK/NACK causes a relatively light load, the PUSCH R1 area taken as PUSCH is used for transmitting the UL data, while in sub-frame 7, the ACK/NACK causes a relatively heavy load, the frequency domain which is identical with the PUSCH R1 area in sub-frame 8 is taken as the PUCCH and used for transmitting the control information. At present, in the UL data transmission of the PUSCH, a frequency hopping method may be used for transmission according to system settings. In sub-frame 8, the PUSCH R1 area is also taken as the PUSCH. The frequency domain resources occupied by the UL data may fall into area 403 in FIG. 4, and may collide with the frequency resources occupied by other UL data in this area after the UL data in this area is processed with the frequency hopping. That is to say, PUSCH402 after the frequency hopping processing may collide with PUSCH401.